Coal Preparation » General
In the primary breakage of a run of mine (ROM) coal to its preparation plant top size, there are three aspects of principle interest to the coal producer:
- Adequate liberation of clean coal from mineral matter to maximise the yield of coal meeting product specifications.
- Maximum yield with minimum concomitant generation of fines.
- Effective breakage to the plant top size at the lowest capital and operating cost.
The aim of this project was to establish the impact of low and high energy breakage of run of mine (rom) coal to prepare coal preparation plant feed. The large particle size of ROM coal required a novel approach to obtaining and processing the samples required for the investigation. This was assisted by the application of gy's sampling theory and a satisfactory compromise was achieved between sample size and experimental handleability.
The shumar 30x60rb secondary crusher and the abon 6/160 hss roll sizer were used for the high and low speed crushers respectively. The equipment manufacturers assisted with the experimental program which evaluated crushing at 50 and 25mm settings for the gap width of the rolls.
There appears to be little variation in the amount of fines being generated by the differing crusher systems, but pre-screening of the feed reduced the amount of fines for both machines. For relatively hard coals, the selection of a high or low speed crusher will mainly depend on capital and operating costs. There was an apparent improvement in the washability from all of the crushing steps as indicated by the ash value of the float 1.4 material. The best result was obtained with a primary crush to 50mm, screening at 25mm and then crushing the plus 25mm material to nominally minus 25mm. The yield was about 65% by mass at an ash value of 8%adb. It is recommended that this opportunity for washability improvement be the subject of further investigation.
A model was developed which provided a good description of all the data examined. It is recommended that its potential is further tested by re-examining the large body of data in the cmte coal breakage program covering an extensive range of coal rank and types. The parameters for the model can be determined from the crusher feed and product size distributions. This would allow the impact of changing the gap width and varying ROM size distributions to be estimated. The potential outcome is improved determination of plant feed characteristics of differing ROM coals.